© 1988 Heron Publishing—Victoria, Canada
Effects of hypoxia and elevated carbon dioxide concentration on water flux through Populus roots
Barbara Smit and Matt Stachowiak
Center for Urban Horticulture GF-15, University of Washington, Seattle, WA 98195, USA / Received April 6, 1987
Summary
Restricted gas exchange between the rhizosphere and aerial environment reduces the concentration of oxygen (O2) and elevates the concentration of carbon dioxide (CO2) in the root zone, thereby leading to increased resistance to root water uptake. In this study, the effects of hypoxia and
20% CO2 on water flux (Jv) through roots of hybrid poplar (Populus trichocarpa Torr. & A. Gray × P. deltoides Bartr. ex Marsh) were measured in detached root systems under pressure in solution culture. Because stomata closed and there
was no change in foliar water potential in hypoxic plants, root resistance was measured in detached systems as opposed to
using whole plant measurements. However, under aerated conditions root resistance values were similar in intact plants and
excised roots.
Water fluxes through pressurized root systems treated with nitrogen and low oxygen (< 2% O2), elevated CO2 (20% CO2), and low O2 with elevated CO2 concentrations were reduced to 40, 51 and
58%, respectively, of Jv of plants aerated with ambient air. Reductions in Jv occurred more rapidly in response to elevated CO2 than to low O2 concentrations. The effects of low O2 and elevated CO2 were not additive. Changes in pH that resulted from elevated CO2 concentrations did not account for the reduction in Jv. When root systems of intact plants were pretreated for 24 or 48 h with low O2 concentration, Jv measured on pressurization was reduced by 33 and 48%, respectively, compared to aerated roots. Stomatal conductance was also
reduced, however, so leaf water potential of plants with hypoxic roots were similar to those of aerated controls.
